The purpose of this research activity is to conduct routine serum-based monitoring of the prevalence of atypical strains of HIV among persons recently diagnosed with HIV in Los Angeles County and to evaluate the feasibility and efficiency of using dried blood spots (DBS) for routine surveillance of atypical strains of HIV where serum is not available. Data on the prevalence of drug resistant HIV strains and non-B subtypes in Los Angeles County is critical for the identification of emerging epidemics, the monitoring of trends in HIV transmission, and the targeting of HIV prevention resources. The specific aims of this project are: (1) To monitor the prevalence of HIV drug resistant strains and non-B HIV subtypes in persons newly diagnosed with HIV at (a) HIV testing sites where HIV diagnostic sera can be used for routine surveillance of atypical strains of HIV and (b) HIV testing sites where only DBS are available for routine surveillance of atypical strains of HIV; (2) To compare the logistics, resources, and staff time needed to collect and process specimens in sites where HIV diagnostic sera can be used for routine surveillance of atypical HIV strains and in sites where only DBS are available; and (3) To compare the results of HIV genotyping performed on serum and DBS specimens obtained from persons newly diagnosed with HIV. The proposed research activity will employ a cross-sectional study design to determine the prevalence of atypical HIV strains among persons newly diagnosed with HIV at publicly funded HIV testing sites in Los Angeles County. To determine the prevalence of atypical HIV strains in the study population, HIV genotyping will be performed on blood specimens, either serum or DBS, obtained from laboratory reserves or directly from study participants.